[unreadable] [unreadable] 'Behavioral inhibition' or 'shyness' among children and adults has been associated with several negative health consequences. Approximately 20% of children are reliably behaviorally inhibited - i.e. they withdraw from novel or unfamiliar circumstances and show greater activation of stress- and fear-associated physiological systems including the hypothalamic-pituitary-adrenal (HPA) axis. The proposed research will test whether a behavioral trait identified as neophobia in the commonly used laboratory rat (Rattus norvegicus) is analogous to the trait identified as behavioral inhibition in humans, such that rats could provide an animal model in which to conduct experimental studies on the causes and consequences of this trait. By developing a non-human model of behavioral inhibition, it becomes possible to conduct life span developmental and experimental studies to determine the environmental and genetic origins of the trait, and to determine potential remedial interventions if the trait is found to be primarily disadvantageous to health. This research will be conducted with Sprague-Dawley rats, a strain of rat in which naturally-occurring variance exists in individual willingness to explore a novel environment and for which stress hormones (glucocorticoids) released by adrenal cortex are related to this trait. The research will assess the stability of this behavioral trait by measuring individual rats' behavioral responses across different conditions and across time, and will measure the dynamics of glucocorticoid production to determine if inhibited individuals experience longer, more chronic, elevations in glucocorticoids, thus making them more prone to health problems. Finally, given the importance of early peer social interactions on personality formation, the research will use an experimental study to determine how peri-pubertal social interactions affect the development of neophobia. This research will provide the basis for future research on the development and long-term consequences of behavioral inhibition / shyness. [unreadable] [unreadable]